This objective of this proposal is to identify genetic differences between cancer cells that lie dormant in the bone and those that have ?re-awakened? from a dormant state, and to discover the mechanisms responsible. These studies will identify potential therapeutic targets for the nearly 3 million breast cancer patients currently in remission. There is sufficient evidence that hypoxia (a lack of oxygen) stimulates parathyroid hormone-related protein (PTHrP) and inhibits leukemia inhibitor factor (LIF) signaling in breast cancer cells, which may control the re-awakening process. Deletion of LIFR or over-expression of PTHrP results in the conversion of weakly metastatic breast cancer cells to invasive and highly metastatic cells, which leads to the hypothesis that hypoxia promotes bone metastasis in part through down-regulation of LIFR signaling, which stimulates cancer cells to exit dormancy through vascular endothelial growth factor (VEGF) production. This will be tested using several current breast cancer models in which LIF and PTHrP signaling is disrupted to determine their effect on mRNAlevel changes in breast cancer cells as they evolve from dormant to proliferative. Weakly bone metastatic human MCF-7 and mouse D2.0R cancer cell lines will be used as models of breast cancer dormancy in bone. These cells will be driven out of dormancy in vivo through LIF signalling inhibition and PTHrP over-expression. GFPlabelled breast cancer cells will be dyed with RFP that is lost as cells divide, and these tags will be used to fractionate dormant vs post-dormant (proliferative) cells in the bone marrow for RNA sequencing. The proposal will also examine the role of hypoxia inducible factor (HIF) and LIF signaling at the primary tumor site on bone metastasis using the MMTV-PyMT spontaneous model of breast cancer and mice lacking HIF1? and HIF2? in the mammary gland. Dr. Johnson?s immediate goal is to establish a dormancy signature for breast cancer cells in the bone that is consistent across multiple models. The proposed project will identify genetic aberrations in dormant vs proliferative cells and lay the foundation for Dr. Johnson to establish an independent laboratory at an academic research institution. Her research training program includes attendance at relevant seminars, workshops, and courses hosted by Stanford University, as well as oversight from co-mentors and a respected career advisory committee she has formed to monitor both career and scientific development.